At the search meeting with mconnor today, we had a go/no-go for form history on 78 release and decided to go. So we should set browser.urlbar.maxHistoricalSearchSuggestions to 2 unconditionally: https://searchfox.org/mozilla-central/rev/598e50d2c3cd81cd616654f16af811adceb08f9f/browser/app/profile/firefox.js#284

We also talked about how to handle form history wrt to prefs. In the long term, we want to reorganize the prefs UI and add a way for users to toggle form history on and off. I'll file another bug for that and mark it as a see-also. In the short term including on 78, we want form history to behave like remote suggestions wrt to prefs. So if a user has remote suggestions enabled, then form history will also be enabled, and vice versa. This is in addition to browser.urlbar.maxHistoricalSearchSuggestions. The logic for determining whether remote suggestions are enabled is here, so we'll probably want all of that for form history too: https://searchfox.org/mozilla-central/rev/598e50d2c3cd81cd616654f16af811adceb08f9f/browser/components/urlbar/UrlbarProviderSearchSuggestions.jsm#140

Of course we'll need to uplift this to 78.

We didn't talk specifically about private browsing in the meeting today, but we
did say we want to treat form history like remote suggestions, so this patch
checks queryContext.allowSearchSuggestions and queryContext.isPrivate in
addition to the browser.urlbar.suggest.searches and
browser.search.suggest.enabled prefs.

https://treeherder.mozilla.org/#/jobs?repo=try&revision=2f53cfc30cde9b93f73355c567f347edcb493e0f

https://hg.mozilla.org/mozilla-central/rev/4de50792fb20

Beta 78 try push: https://treeherder.mozilla.org/#/jobs?repo=try&revision=b4c75eb297bcd130bf78c0ac5077efdb803468d2

Comment on attachment 9154454 [details]
Bug 1643475 - Enable form history / historical searches on 78 release and put them behind the same prefs as remote suggestions.

Beta/Release Uplift Approval Request

• User impact if declined: This patch enables search suggestions from history on beta 78. We'll have to wait until 79 to ship this feature if this is declined.
• Is this code covered by automated tests?: Yes
• Has the fix been verified in Nightly?: No
• Needs manual test from QE?: Yes
• If yes, steps to reproduce: 1. Type "test" in the urlbar and hit enter to do a search.

2. Type "tes" (no trailing "t") in the urlbar. As you are typing, there should be a "test" suggestion result in the urlbar view, and it should have a clock icon to indicate it's a suggestion from history.
3. Press enter or click the "test" suggestion from history. Firefox should load a new "test" search on the default search engine.
4. Open about:preferences#search and uncheck "Show search suggestions in address bar results".
5. Type "tes" in the urlbar again. There should not be a "test" suggestion result.
6. In about:preferences#search, check "Show search suggestions in address bar results" and uncheck "Provide search suggestions".
7. Type "tes" again. There should not be a "test" suggestion result.
8. In about:preferences#search, check "Provide search suggestions".
9. Type "tes" again. There should be a "test" suggestion result.
10. Open a private window and type "tes". There should not be a "test" suggestion result.
11. In about:preferences#search, check "Show search suggestions in Private Windows".
12. In the private window, type "tes". There should be a "test" suggestion result from history.

• List of other uplifts needed: None
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): This code is covered well by tests and it only affects suggestions in the urlbar.
• String changes made/needed:

Comment 6 doesn't really explain why this can't/shouldn't ride the trains.

Product would like to enable this feature ASAP on 78. We have data from Google that suggests it will increase the number of searches done through the urlbar.

Verified as fixed using the steps from comment 6 with latest Nightly 79.0a1 2020-06-09 under Win 10 64-bit, Ubuntu 18.04 64-bit and Mac OS X 10.15.

Comment on attachment 9154454 [details]
Bug 1643475 - Enable form history / historical searches on 78 release and put them behind the same prefs as remote suggestions.

approved for 78.0b6

https://hg.mozilla.org/releases/mozilla-beta/rev/1ebfd5520c6e

I can confirm this fix has landed on beta as well.
I verified used Fx 78.0b6 on Windows 10 x64 and macOS 10.13.